An undercover NYPD officer fatally shot an innocent bystander -- and wounded a suspected armed robber -- during a gun-buy gone awry in Mount Vernon on Friday, police said.

Felix Kumi, 61, of Mount Vernon, died of his wounds at 12:55 a.m. Saturday at Jacobi Medical Center in the Bronx, police said. Kumi, who had been standing behind the suspected robber as the officer fired, was struck twice in his torso, police said.

The father of two was on his way to pick up his car from a nearby repair shop when the shooting happened, said his neighbor, Sharon Johnson, 53, who recalled Kumi as a "very kind, very devoted dad."

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"He always had a smile for you, always had a kind word," said Johnston, adding that Kumi was a devout Jehovah's Witness. "It's so messed up that he was walking past there when the shooting started."

Kumi drove a bus for the Mount Vernon school district for the past 10 years, his daughter, Rachel, 25, told The Journal News. "It's a travesty that this happened," she said.

NYPD Commissioner William Bratton issued a statement Saturday expressing his "profound sorrow and sympathy" for Kumi's family.

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"Mr. Kumi was blameless, and this tragedy has tested and tried his family," Bratton said.

The officer's intended target, a 37-year-old New Jersey man whom police did not identify, was shot three times after he pointed what turned out to be a "replica" .45-caliber handgun toward the officer, police said. The man was taken to Jacobi, where his condition was not known. Charges against him are pending, police said.

The other man involved in the case, suspected gun seller Jeffrey Aristy, 28, of the Bronx, was arrested after fleeing the scene and charged with criminal sale of a firearm and controlled substance, police said. It was not clear whether he had an attorney.

The incident unfolded about 4 p.m. Friday when the undercover officer in the Firearms Investigation Unit got a call from Aristy about guns for sale and met him in the Bronx, police said. Aristy got into the officer's car and told him to drive to Mount Vernon, where they met the unidentified 37-year-old man, who got into the backseat and "pointed a gun at the officer's head while demanding money," police said in a statement.

The officer gave him more than $2,000 in "buy money," after which the robber attempted to flee. The officer then signaled to his backup team and exited his car "in order to engage" the man who had just robbed him, police said.

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The officer fired several times, striking both the 37-year-old suspect and Kumi, police said. Investigators said they found the replica gun, along with the officer's buy money, in the wounded robber's possession.